Fatigue resistance of steel and titanium PVD coated spur gears

The aim of this work is to investigate into the possibility of enhancing the fatigue resistance of CrN-PVD coated components. In particular, PVD coated spur gears were tested and a numerical simulation of crack propagation was carried out. The coating layer microhardness and the residual stresses characterising the surface film were measured. The results obtained were then introduced in a numerical model for predicting the fatigue life procedure of coated gears used in gearboxes for automotive applications. The number of cycles necessary to reach specified crack depths in coated and uncoated steel and titanium spur gears was numerically determined. This represents a powerful tool to predict the fatigue life of coated gears. Benefits induced by the presence of the coating were pointed out. A sensitivity analysis was also carried out: Furthermore, the effects on the fatigue crack propagation of the residual stress gradient (evaluated by means of X-ray measurements), the elastic properties of the bulk material and coating were evaluated.